Laboratory Bioassay Evaluating Peanut Seedlings for Resistance to the Southern Corn Rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae)

The objective of this study was to develop a laboratory bioassay that consistently distinguishes peanut genotypes (Arachis hypogaea L.) based on their potential susceptibility or resistance to the southern corn root-worm (SCR), Diabrotica undecimpunctata howardi Barber, a major soil insect pest of peanut in North Carolina, Virginia, and other states. The susceptibility or resistance of a peanut genotype to the SCR was characterized by the survival, development, and mean weight of the pest after feeding for 14 d on seedlings of different peanut genotypes. An initial 14 d seedling bioassay demonstrated the ability of the technique to separate a susceptible cultivar (NC 7) from a resistant cultivar (NC 6) based on the percentage of SCR that survived after 14 d, the percentages and mean weight of surviving SCR in larvae, prepupae, and pupae. Subsequently, two 14 d seedling bioassays evaluated five additional peanut genotypes that were believed to have some resistance to the SCR (N97059N, N92069L, VA 861101, VT 9506114–1, NC-GP WS 9) along with the susceptible (NC 7) and resistant (NC 6) controls. The final two bioassays were modified to test the differences in the percentages of SCR adults that emerged and the time required for adult emergence after feeding as larvae on the susceptible (NC 7) and resistant (NC 6) peanut seedlings. The 14 d seedling bioassay represents an improvement over earlier seedling bioassays because of its consistent ability to distinguish susceptible and resistant peanut genotypes, and because of the diversity of parameters measured. It consistently separated the susceptible (NC 7) and resistant (NC 6) controls, with one or more of the parameters measured. The breeding line N92069L and the germplasm line NC-GP WS 9 were shown to result in significantly lower survival of SCR and to delay development relative to the susceptible control NC 6. A seedling bioassay where eggs were allowed to develop to the adult stage repeatedly separated NC 7 from NC 6 based on the percentages of adults that emerged. Results indicate the seedling bioassay should be a reliable method for screening large numbers of peanut genotypes before committing the time, space, and labor required for field evaluations. In addition, future peanut breeding programs should consider attempting to introduce the resistance expressed in NC-GP WS 9, N92069L, and N97059N into lines with desirable agronomic characteristics.